The present invention relates generally to improved barrier members, such as "plugs" or "locks" adapted for use in subterranean wells; and more particularly, to improved plugs or locks and associated operating systems, and methods of their use in oilfield tubular members, such as casing or tubing strings.
The use of plugs or locks in oilfield tubular members is well known in the art. A packer-type lock, as particularly described relative to the preferred embodiment herein, is typically intended to be placed in the tubular member, such as a subsurface tubing string, and to securely and sealingly engage the interior wall of the tubing string. Once in place, the lock provides fluid and pressure isolation between sections of the tubing string.
Many such lock systems have been developed in which landing nipples or profiles are provided at points along the tubing string's interior surface, and wherein a lock will be placed in the nipple or profile. However, placement of a lock of this type is limited to those points along the string at which an appropriate nipple or profile is located.
A few plugs are known which are "nippleless" in that they do not require the presence of a nipple or profile to be set within a string or wellbore. Nippleless systems offer the capability to set plugs at substantially any depth or point within a subterranean well. These systems also reduce the need to foresee, at the time tubing or casing is placed, where a packer device will later be needed.
Conventional methods of running and pulling nippleless plugs or locks, however, typically require that actuating power be supplied from the surface to the running or pulling assemblies performing these functions. This requires, therefore, that the tools be run on wireline, rather than slickline (without an electrical conductor), as is used for many other types of well operations. This requirement increases the equipment needs, and the cost of the operation of setting or pulling the plug or lock.
There are techniques which do not rely upon surface-supplied electrical power to set a lock. These systems, however, typically rely upon an explosive charge to set the lock. Rapid setting sequences, and particularly those performed as rapidly as is typically achieved through use of explosive devices are detrimental in that they adversely affect the quality of the setting of each member. For example, slip elements are known to set more securely when they engage tubing or casing in a controlled manner. Further, elastomeric packer elements establish a better seal when the elastomeric material is deformed gradually, and stresses within the-material are thereby allowed to equalize more gradually, thereby minimizing subsequent relaxation of the elastomer, with an accompanying reduction in sealing effectiveness.
Many existing slip designs employ radially segmented slip elements which are urged outward to engage the interior wall of the surrounding tubing string. The slip elements are often separated from each other a significant distance. If the slip is being set in a non-vertical tubing string, the elements may expand non-uniformly resulting in the lock being decentralized within the string. As a result, a pressure differential across the lock will be more likely to result in failure of the lock's slips due to the unequal forces upon the slips and packing element around the circumference of the lock.
Conventional designs for packer-type locks offer a further disadvantage in removal operations. After a packer-type lock is set and subjected to a period of high temperature and pressure, the packing element will typically achieve some degree of "set" toward the expanded state. This "set" of the packing element may also be considered as an absence of "memory" of the packing element for its original form. The distended exterior diameter may make removal of the lock difficult as it reduces the fluid bypass around the lock, and may provide difficulty in clearing areas of relatively restricted diameter, such as an uphole nipple or profile.
In a related aspect, retrieving or "pulling" operations for locks typically rely upon engaging a set lock with a wireline device and pulling or jarring the lock upward in an attempt to dislodge it from within the tubing string. This technique is not always successful and sometimes results in either damage or "hanging up" of the lock within the tubing string.
Accordingly, the present invention provides a new barrier device, such as a lock (or "plug") and associated methods and apparatus for setting and pulling the barrier device without the requirement of a nipple or profile; and which, in a preferred embodiment, facilitates both controlled, gradual, setting of the device, and release of the device without jarring.